Conventionally, as a technique for reducing noise that occurs if a recovery current is reduced, there has been a technique of constituting a semiconductor device by connecting in parallel a Schottky barrier diode and a silicon PiN diode, which are based on semiconductor material having a wide band gap, to reduce the noise (refer to Japanese Patent No. 4980126, for example).
A power semiconductor module is used in a wide range of fields as an element to constitute an inverter. Especially, a power semiconductor module, using a silicon IGBT (Insulated Gate Bipolar Transistor) chip for a switching device and a silicon PiN diode chip for a diode element, is superior in terms of a high breakdown voltage and low-loss properties, and thus is used in a wide range of fields such as railroads and household electrical appliances. Additionally, in recent years, there are some cases to use for a diode device a Schottky barrier diode (hereinafter, referred to as SBD), an MPS (Merged PiN Schottky), a PiN diode, or the like, which is based on semiconductor material having a wide band gap, such as silicon carbide (SiC), (hereinafter, these diodes are simply referred to as SiC diodes), in order to reduce loss. However, when these diodes are used to reduce a recovery current, noise may be generated due to resonance between a capacitance and inductance components within a subject circuit. As a countermeasure against this noise, Japanese Patent No. 4980126 discloses a technique for implementing a semiconductor device in which an SBD based on semiconductor material having a wide band gap and a silicon PiN diode are connected in parallel to reduce the noise.
The present inventors have made studies on further noise reduction in the semiconductor device including an SiC diode and a silicon PiN diode connected in parallel, to find a problem as described below.
In a conventional configuration, it is contemplated that a forward voltage across the silicon PiN diode chip is lower than that across the SiC diode chip, especially at a high temperature (e.g., a junction temperature of 150° C.), and this causes a current to concentrate into the silicon PiN diode chip to reduce the amount of power cycle resistance. In addition, if a silicon PiN diode having a high forward voltage is used to avoid the current from mainly flowing to the silicon PiN diode, a current flowing through the silicon PIN diode chip is reduced in a conductive state to cause a recovery current to be reduced, to lose effects of a noise reduction.
The studies made by the present inventors have revealed a calculation result that, in the conventional configuration, a current flowing through the silicon PiN diode chip is 1.7 times that through the SiC diode chip under the condition of the junction temperature of 150° C.
Hence, the present invention is intended to provide a technique that allows for loss reduction and noise reduction while preventing a current from concentrating into a specific chip.